The growth and development of the prostate gland is tightly regulated by sex steroids during embryonic and adult life. To understand the cellular mechanisms of this regulation, this laboratory has developed a cell-cell interaction model in which we observed the proliferation of prostatic epithelial and stromal cells is differentially regulated by androgen and estrogen, respectively. Sex steroids generally are not considered as direct mitogens; most probably, they stimulate growth and gene expression through the induction of soluble growth factors and/or extracellular matrices, which are considered central mediators of sex steroid action in cell growth regulation. The purpose of this proposal is to develop a molecular approach for cloning, characterizing, and expressing mesenchymal factors induced by androgen and estrogen in a chimeric model of prostate growth. Specific Aims Are: Specific Aim I: A chimeric prostate tumor model will be established in athymic mice using a cell- cell recombination approach. Initially, a fetal rat urogenital sinus mesenchymal cell line will be used as a growth inductor for LNCaP and primary human prostatic epithelial cells. Additional human mesenchymal cell lines will be derived from fetal and adult prostate to investigate the possibility of developing chimeric human prostate organs. These models will be used to study the effects of androgen and estrogen on epithelial and stromal proliferation and gene expression in vivo. The in vivo models are necessary because sex steroids seldom have induced significant proliferative and gene expression responses of prostatic epithelial and stromal cells in vitro. Specific Aim II: The androgen and estrogen-responsive mesenchymal cDNAs from the chimeric prostate organ models will be cloned and characterized by a differential display method. cDNAs identified will be used as mesenchymal markers. In addition, the molecular mechanism of hormone regulation will be investigated. Selected cDNAs will be tested for their in vitro and in vivo (transgene) growth regulating properties. Specific Aim III: The expression of mesenchyme-associated genes in human prostate tumors and in the experimental models of prostate tumors will be characterized. The expression of factors such as keratinocyte growth factor, androgen- induced growth factor, and a novel bone stromal factor recently identified by this laboratory will be evaluated in both human prostate tissues and in the chimeric prostate organs. The transduction of the latter factor to either fibroblasts or epithelial cells will be accomplished by the highly efficient MFG retroviral vector and the biologic activity of the transgene will be evaluated in cell or tissue recombination studies. This study is expected to extend the understanding of regulation of prostate growth by androgen and estrogen. The molecular approach to delineating specific mesenchymal factors that may serve as mediators between mesenchymal and epithelial cells could lead to new therapeutic and preventative measures for prostate diseases.